An RA procedure allows a UE to access a network using the Random Access Channel (RACH). The RA procedure is part of the Medium Access Control (MAC) protocol specification.
FIG. 1 exemplarily shows the RA procedure in an exemplary Long Term Evolution (LTE) network 100 comprising a UE 1001 and an eNB 1002. In a first step S1, the UE 1001 sends an RA preamble which allows the eNB 1002, inter alia, to estimate the timing advance for the UE 1001. In step S2, the eNB 1002 transmits a scheduling RA response containing the uplink resources to be used in the next step as well as the timing estimate based on the transmission in the first step S1. The index of the detected RA preamble sequence is also sent in this message.
Step S3 comprises transmitting a Message 3 (Msg3) which contains, among others, a unique identity (ID) of the UE 1001. In step S4, a Message 4 (Msg4) is used for contention resolution, since in step S1 it is possible that multiple UEs 1001 with the same preamble had started a RA procedure. In this step S4, each UE 1001 receiving this message compares its own ID sent in step S3 to the ID inserted in Msg4. The UE 1001 that detects its own ID in Msg4 is considered as the “winner” of the RA procedure. As shown in FIG. 1, in steps S3 and S4, the messages are accompanied by a Hybrid Automatic-Repeat-Request (HARQ).
As a starting and/or triggering condition, the UE 1001 can initiate an RA procedure in several cases, such as:                Case 1: initially accessing the network when a Radio Resource Control (RRC) connection is established (i.e., the UE 1001 transits from the mode RRC_IDLE to the mode RRC_CONNECTED);        Case 2: when a handover occurs, establishing an uplink synchronization (i.e., RRC reconfiguration);        Case 3: after a radio link failure, re-establishing the RRC connection (i.e., RRC re-establishment);        Case 4: restoring an uplink synchronization when the uplink is not synchronized and the UE 1001 is in the RRC_CONNECTED mode, and uplink (UL) or downlink (DL) data arrives to be transmitted; and/or        Case 5: requesting for an UL grant for the UE 1001 having no dedicated scheduling request resource configured on the Physical Uplink Control Channel (PUCCH).        
The main objective in all of the above cases 1 to 5 is to establish UL synchronization. The RA procedure also aims at assigning a unique ID to the UE 1001 when a new RRC connection is established.
However, in LTE, the terminal or UE 1001 may use contention-free RA, where the eNB 1002 allocates a dedicated RA preamble to the UE 1001 and thereby prevents contention. Thus, in this case, only steps S1 and S2 shown in FIG. 1 are applicable. The contention-free RA is supported in case of handovers or when DL data traffic has initiated the RA procedure. This type of RA is faster than the contention-based procedure, thus it is applicable in case of handovers which are time-sensitive.
In LTE, there is one measurement report that is related to the RACH procedure, namely the so-called RACH report. As defined in sections 5.5 and 5.6 of 3GPP TS 36.331, Radio Resource Control (RRC); Protocol specification, V11.2.0 of 3 Jan. 2013, the RACH report logs, inter alia:                the last successful random access attempt including both RRC setups and other RACH attempts,        a number of random access preambles sent before success, and        whether there was contention detected for any of the Msg3 transmissions.        
However, the existing measurement does not report such information that could be used to measure and monitor the overall performance of RACH. The UE 1001 reports failures only for those RACH attempts that are related to RRC connection setup (i.e., it does not include RACH failures once in RRC_CONNECTED mode). Furthermore, the eNB 1002 does not report similar RACH related measurements that could help identifying root causes of different RACH failures.